The world production of shellfish of various crustacea species including crab, shrimp, prawns, crayfish and lobsters has increased enormously in recent years. In general, only a small portion, 20-30 percent, of the live weight of these crustacea species is considered suitable for human food, namely the fleshy tissue found in portions of the body and major appendages. The balance, comprising viscera, and the exoskeleton or "shell" is usually discarded as waste although in some instances it is dried, ground and marketed as "shellfish meal" for use as animal feed or fertilizer.
An indication of the shellfish production in a few countries of the world is indicated in the following TABLE I.
TABLE I ______________________________________ SOME SHELLFISH PRODUCTION DATA - 1968 Live Weight Millions of Country Species Pounds ______________________________________ Alaska King Crab 30 Tanner Crab 7 Dungeness Crab 20 Shrimp 30 U.S. (landings) Shrimp 300 (imports) Shrimp 350 (landings) Dungeness Crab 20 (landings) Blue Crab 40 (landings) Northern Lobster 48 Canada (landings) Northern Lobster 37 Mexico (U.S. Imports) Shrimp 84 India (U.S. Imports) Shrimp 37 South Africa (U.S. Imports) Spiny Lobster 32 Australia (U.S. Imports) Spiny Lobster 29 ______________________________________
The concerned species of crustacea have a number of common characteristics and common problems. For examply, the edible portion of crustacea is normally 20-30 percent of the live weight with the rest of the shellfish of crustacea being waste. While the edible portion of the shellfish and in some instances, partially processed products, e.g., "heads-off" shrimp, lobster tails, King crab leg-in-shell sections, etc., command good prices with firm demand in the world markets, the recovery of the waste has been uneconomical, or, at best, marginal for only a small portion of the available tonnage of waste. As a result, wastes are often dumped into waterways adjacent to the processing plants; and, in localities where a concentration of processing activity occurs, serious pollution problems prevail with an increase in the bacteria count of the adjacent waterways.
One example of a major shellfish waste pollution situation is found in Kodiak, Alaska. Here, about 60% of the shellfish industry of Alaska is concentrated with the annual catch figures, in live weight, as indicated in the following TABLE II:
TABLE II ______________________________________ SHELLFISH CATCH IN POUNDS ______________________________________ King crab 40-60 million pounds Other crab species 20-30 million pounds Shrimp 20-30 million pounds Total catch 80-120 million pounds Waste 50-70 million pounds ______________________________________
There are approximately fifteen processing plants in the Kodiak, Alaska, area. No attempt is made to recover the shellfish waste of crustacea and these wastes are dumped into the harbor adjacent to the processing plants. As a result, there is pollution of the water in the harbor. This pollution is a nuisance to the community and a hazard to the industry itself through the growth of bacteria in the harbor waters, and, also, in the live tanks.
In some of the fisheries centers there is produced shellfish meal from the shellfish waste of crustacea. In general, shellfish waste meals have limited markets due to their high mineral and chitin content. This limits levels at which the shellfish waste meals can be fed to farm animals and to poultry. In the Kodiak area in particular, it has not been economical to process the shellfish waste. There is a lack of local markets for the feed materials and the high freight costs to potential consuming areas makes it uneconomical to process shellfish waste of crustacea into shellfish waste meal.
Markets for "shellfish meal" are marginal since the crude product has intrinsic properties which limit its value. The exoskeleton of the shell of crustacea, usually amounting to 40-60 percent of the waste is about half mineral matter (calcium carbonate with some calcium phosphate), the remainder being chitin and protein. Chitin is indigestible for poultry and livestock and can cause intestinal irritation. Thus, only the protein is of real value as a feed material and the other components of shellfish meal are undesirable diluents detracting from the feed value.
As a result of this background, a study was made of the possibility of processing crustacea waste. From this study this invention and process has been made.
If the waste can be separated into its components, mineral matter, chitin, protein and carotenoid pigments of considerably greater value can be recovered. Chitin is a source of valuable polymeric carbohydrate material having many potential uses and the protein of the exo-skeleton of crustacea is of high nutritional quality having a good balance of essential amino acids. In this manner it is different in character from the collagen, keratin and gelatin usually found in animal waste products.
While a minor portion of the protein in crustacea waste is unremoved flesh and visceral material, the major part is protein laid down with chitin and mineral matter in the formation of the exoskeleton. This is largely chemically bound to the chitin and sometimes to carotenoid pigments.
In crustacea, the shell comprise a matrix of protein chemically combined with chitin mixed with calcium carbonate. The protein is not free or readily available. In order to remove the protein, the shell of the crustacea is treated with an alkaline aqueous solution to penetrate the interstices of the shell matrix to rupture the bond between protein and chitin. The protein is dissolved in the alkaline aqueous solution. In the crustacea waste there is some free protein occluded on the shell, but most of the free protein in the crustacea waste has been removed by washing. The major portion of the protein is bound within the shell matrix.
A more detailed resume of the crustacea exoskeleton is presented in The Physiology of Crustacea, edited by Talbot H. Waterman, Department of Zoology, Yale University, Volume 1, "Metabolism and Growth", Academic Press, New York and London, 1960, and, in particular, on page 449 wherein it is stated: